arXiv subjects

Robert Fleischer

Publications and source records attributed to Robert Fleischer.

At least 73 records · Page 4Linked to original sources

arXiv2011

Anatomy of $B^0_{s,d} \to J/ψf_0(980)$

The $B^0_s\to J/ψf_0(980)$ decay offers an interesting experimental alternative to the well-known $B^0_s\to J/ψϕ$ channel for the search of CP-violating New-Physics contributions to $B^0_s$--$\bar B^0_s$ mixing. As the hadronic structure of the $f_0(980)$ has not yet been settled, we take a critical look at the implications for the relevant observables and address recent experimental data. It turns out that the effective lifetime of $B^0_s\to J/ψf_0(980)$ and its mixing-induced CP asymmetry $S$ are quite robust with respect to hadronic effects and thereby allow us to search for a large CP-violating $B^0_s$--$\bar B^0_s$ mixing phase $ϕ_s$, which is tiny in the Standard Model. However, should small CP violation, i.e. in the range $-0.1\lsim S\lsim 0$, be found in $B^0_s\to J/ψf_0(980)$, it will be crucial to constrain hadronic corrections in order to distinguish possible New-Physics effects from the Standard Model. We point out that $B^0_d\to J/ψf_0(980)$, which has not yet been measured, is a key channel in this respect and discuss the physics potential of this decay.

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arXiv2011

In Pursuit of New Physics with B Decays

Decays of B mesons offer interesting probes to search for physics beyond the Standard Model. Thanks to the data taking at the LHC, we are at the beginning of a new era of precision B physics. I will discuss recent developments concerning the analyses of promising channels to search for signals of New Physics at the LHC, B^0_s -> J/psi phi, B^0_s -> K^+K^- and B^0_s -> mu^+ mu^-.

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arXiv2011

Extraction of the weak angle gamma from B to charm decays

We give a summary of the discussions in Working Group V of the CKM2010 workshop dealing with determinations of the angle gamma of the unitarity triangle of the Cabibbo-Kobayashi-Maskawa matrix from B-meson decays into charmed final states.

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arXiv2011

Tests of Factorization and SU(3) Relations in B Decays into Heavy-Light Final States

Using data from the B factories and the Tevatron, we perform tests of how well non-leptonic B decays of the kind B -> D^{(*)}_{(s)} P, where P is a pion or kaon, are described within the factorization framework. We find that factorization works well - as is theoretically expected - for color-allowed, tree-diagram-like topologies. Moreover, also exchange topologies, which have a non-factorizable character, do not show any anomalous behavior. We discuss also isospin triangles between the B -> D^{(*)} pi decay amplitudes, and determine the corresponding amplitudes in the complex plane, which show a significant enhancement of the color-suppressed tree contribution with respect to the factorization picture. Using data for B -> D^{(*)} K decays, we determine SU(3)-breaking effects and cannot resolve any non-factorizable SU(3)-breaking corrections larger than \sim 5%. In view of these results, we point out that a comparison between the \bar B^0_d -> D^+π^- and \bar B^0_s -> D_s^+π^- decays offers an interesting new determination of f_d/f_s. Using CDF data, we obtain the most precise value of this ratio at CDF, and discuss the prospects for a corresponding measurement at LHCb.

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arXiv2010

A Fresh Look at B_{s,d} -> pi pi, pi K, K K Decays

Using updated measurements and SU(3)-breaking form factors, we have a detailed look at the B_d -> pi^+ pi^-, B_s -> K^+ K^- and B_d -> pi^\mp K^\pm, B_s -> pi^\pm K^\mp systems. The corresponding decays are related to each other by the U-spin symmetry of strong interactions and offer determinations of the angle gamma of the unitarity triangle. In the former case, we obtain gamma=(68.3^{+4.8}_{-5.7}^{+5.0}_{-3.7}) deg, which is in excellent agreement with the Standard-Model fits of the unitarity triangle. The first errors correspond to experimental input uncertainties, while the latter are an estimate of U-spin-breaking effects. In view of this result, large CP-violating new-physics effects at the amplitude level are excluded. However, the effective B_s -> K^+ K^- lifetime and the mixing-induced CP violation in this channel offer interesting probes for New Physics in B^0_s-\bar B^0_s mixing. In the case of the B_d -> π^\mp K^\pm, B_s -> pi^\pm K^\mp system, using additional information from B^\pm -> π^\pm K, we obtain a bound of gamma \leq (71.8^{+5.4}_{-4.3}) deg, and the range 24 deg \leq gamma \leq 71 deg. We perform also tests of the U-spin symmetry and do not find any indication for large non-factorizable corrections.

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arXiv2010

Extracting gamma and Penguin Parameters from B^0_s -> J/psi K_S

The B^0_s -> J/psi K_S decay has recently been observed by the CDF collaboration and will be of interest for the LHCb experiment. It is the U-spin partner of the golden B^0_d -> J/psi K_S channel and offers a determination of the angle gamma of the unitarity triangle. Moreover, it allows us to control the hadronic penguin effects in the extraction of the B^0_d-\bar B^0_d mixing phase phi_d through a measurement of CP violation in B^0_d^0 -> J/psi K_S. We discuss the picture emerging for these measurements from an LHCb feasibility study. While LHCb will be able to extract gamma from the CP violation in B^0_d -> J/psi K_S, the main application of this channel will be the determination of hadronic penguin parameters. Such an analysis is actually needed in order to fully exploit LHCb's impressive experimental precision for the determination of phi_d from B^0_d -> J/psi K_S. We give also the target regions for the effective lifetime of B^0_s -> J/psi K_S and its CP-violating observables for improved measurements by CDF and the 2011 data taking at LHCb.

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arXiv2010

In Pursuit of New Physics with B^0_s -> K^+K^-

The B^0_s -> K^+K^- decay is the U-spin partner of B^0_d -> pi^+π^- and allows a determination of the angle gamma of the unitarity triangle of the Cabibbo-Kobayashi-Maskawa matrix. Using updated information on the branching ratio and the relevant hadronic form factors, we discuss the picture that emerges for gamma from the currently available data, which is in good agreement with the fits of the unitarity triangle. We point out that the B^0_s -> K^+K^- decay also offers interesting probes to search for new physics in B^0_s-\bar B^0_s mixing, thereby complementing the well-known B^0_s -> J/psi phi analyses. The relevant observables are the effective lifetime of this channel and its mixing-induced CP asymmetry. We calculate correlations between these quantities and the CP-violating B^0_s-\bar B^0_s mixing phase, which serve as target regions for improved measurements at the Tevatron and the early data taking at the LHCb experiment. Finally, we discuss the expected situation for the optimal determination of gamma at LHCb, exploiting precise measurements of the CP violation in B^0_s -> K^+K^-.

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arXiv2010

B Physics in the LHC Era: Selected Topics

We have just entered a new round in the testing of the flavour sector of the Standard Model through high-precision measurements of B-meson decays. A particularly exciting aspect is the exploration of the B_s-meson system at LHCb. We focus on two particularly promising probes of new physics which may give us first solid evidence for New Physics at the LHC: the strongly suppressed rare decay B_s^0 -> mu^+mu^- and CP-violating effects in the B_s^0 -> J/psi phi channel. We discuss recent theoretical developments related to these measurements and shall also sketch other highlights of the B-physics programme in the LHC era.

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arXiv2010

Extracting gamma and Penguin Topologies through CP Violation in B_s^0 -> J/psi K_S

The B_s^0 -> J/psi K_S decay has recently been observed by the CDF collaboration and will be of interest for the LHCb experiment. This channel will offer a new tool to extract the angle gamma of the unitarity triangle and to control doubly Cabibbo-suppressed penguin corrections to the determination of sin(2beta) from the well-known B_d^0 -> J/psi K_S mode with the help of the U-spin symmetry of strong interactions. While any competitive determination of gamma is interesting, the latter aspect is particularly relevant as LHCb will enter a territory of precision which makes the control of doubly Cabibbo-suppressed Standard-Model corrections mandatory. Using the data from CDF and the e^+e^- B factories as a guideline, we explore the sensitivity for gamma and the penguin parameters and point out that the B_s^0-\bar B_s^0 mixing phase phi_s, which is only about -2 deg in the Standard Model but may be enhanced through new physics, is a key parameter for these analyses. We find that the mixing-induced CP violation S(B_s^0 -> J/psi K_S) shows an interesting correlation with sin(phi_s), which serves as a target region for the first measurement of this observable at LHCb.

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arXiv2010

New Strategy for B_s Branching Ratio Measurements and the Search for New Physics in B^0_s -> mu^+ mu^-

The LHCb experiment at CERN's Large Hadron Collider will soon allow us to enter a new era in the exploration of B_s decays. A particularly promising channel for the search of "new physics" is B^0_s -> mu^+ mu^-. The systematic key uncertainty affecting the measurement of this -- and in fact all B_s-decay branching ratios -- is the ratio of fragmentation functions f_d/f_s. As the presently available methods for determining f_d/f_s are not sufficient to meet the high precision at LHCb, we propose a new strategy using \bar B^0_s -> D_s^+ pi^- and \bar B^0_d -> D^+ K^-. It allows us to obtain a lower experimental bound on BR(B^0_s -> mu^+ mu^-) which offers a powerful probe for new physics. In order to go beyond this bound and to determine f_d/f_s with a theoretical precision matching the experimental one it is sufficient to know the SU(3)-breaking correction to a form-factor ratio from non-perturbative methods at the level of 20%. Thanks to our strategy, we can detect new physics in B^0_s -> mu^+ mu^- at LHCb with 5 sigma for a branching ratio as small as twice the Standard-Model value, which represents an improvement of the new-physics reach by about a factor of two with respect to the current LHCb expectation.

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arXiv2008

Benchmarks for the New-Physics Search through CP Violation in B^0->pi^0 K_S

Using isospin relations, we predict the Standard-Model correlation between S_{pi^0 K_S}=(sin 2beta)_{pi^0 K_S} and A_{pi^0 K_S}, the mixing-induced and direct CP asymmetries of B^0-> pi^0 K_S. The calculation uses flavour SU(3) only to fix the isospin-3/2 amplitude through the B^\pm->pi^\pm pi^0 branching ratio, and thus has a small irreducible theoretical error. It can reach percent level precision thanks to expected future lattice-QCD progress for the calculation of the relevant SU(3)-breaking form-factor ratio, and serves as a benchmark for new-physics searches. We obtain an interesting picture in the A_{pi^0 K_S} - S_{pi^0 K_S} plane, where the current experimental data show a discrepancy with the Standard Model, and comment on the direct CP asymmetries of B^0->pi^-K^+ and B^+ -> pi^0 K^+. A modified electroweak penguin with a large new CP-violating phase can explain the discrepancy and allows us to accommodate also the corresponding data for other b->s penguin-dominated decays.

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arXiv2008

Precision Physics with B^0_s -> J/psi phi at the LHC: The Quest for New Physics

CP-violating effects in the time-dependent angular distribution of the B^0_s -> J/psi[-> ell^+ ell^-] phi[-> K^+K^-] decay products play a key role for the search of new physics. The hadronic Standard-Model uncertainties are related to doubly Cabibbo-suppressed penguin contributions and are usually assumed to be negligibly small. In view of recent results from the Tevatron and the quickly approaching start of the data taking at the LHC, we have a critical look at the impact of these terms, which could be enhanced through long-distance QCD phenomena, and explore the associated uncertainty for the measurement of the CP-violating B^0_s-\bar B^0_s mixing phase. We point out that these effects can actually be controlled by means of an analysis of the time-dependent angular distribution of the B^0_s -> J/psi[-> ell^+ ell^-] \bar K^{*0}[-> pi^+ K^-] decay products, and illustrate this through numerical studies. Moreover, we discuss SU(3)-breaking effects, which limit the theoretical accuracy of our method, and suggest internal consistency checks of SU(3).

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arXiv2008

The Golden Modes B^0 -> J/psi K_{S,L} in the Era of Precision Flavour Physics

The B^0 -> J/ψK_{S,L} channels are outstanding probes of CP violation. We have a detailed look at the associated Standard-Model uncertainties, which are related to doubly Cabibbo-suppressed penguin contributions, and point out that these usually neglected effects can actually be taken into account unambiguously through the CP asymmetries and the branching ratio of the B^0 -> J/ψpi^0 decay. Using the most recent B-factory measurements, we find a negative shift of the extracted value of beta, which softens the tension in the fits of the unitarity triangle. In addition, this strategy can be used to constrain a possible new-physics phase in B^0-\bar B^0 mixing. The proposed strategy is crucial to fully exploit the tremendous accuracies for the search for this kind of new physics that can be achieved at the LHC and future super-flavour factories.

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arXiv2008

Flavour Physics and CP Violation: Expecting the LHC

The starting point of these lectures is an introduction to the weak interactions of quarks and the Standard-Model description of CP violation, where the central role is played by the Cabibbo-Kobayashi-Maskawa matrix and the corresponding unitarity triangles. Since the B-meson system governs the stage of (quark) flavour physics and CP violation, it is our main focus: we shall classify B-meson decays, introduce the theoretical tools to deal with them, investigate the requirements for non-vanishing CP-violating asymmetries, and discuss the main strategies to explore CP violation and the preferred avenues for physics beyond the Standard Model to enter. This formalism allows us then to discuss important benchmark modes, where we will also address the question of how much space for new-physics effects in the B studies at the LHC is left by the recent experimental results from the B factories and the Tevatron.

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arXiv2008

Prospects for B-Decay Studies at the LHC

In this decade, there are huge efforts to explore B-meson decays, which offer interesting probes to test the quark-flavour structure of the Standard Model and to search for signals of new physics. Exciting new perspectives for these studies will soon arise at the LHC, where decays of $B^0_s$ mesons will be a key target of the B-physics programme. We will discuss theoretical aspects of various benchmark channels and address the question of how much space for new-physics effects in their observables is left by the recent experimental results from the B factories and the Tevatron.

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arXiv2007

Studying New Physics Amplitudes in Charmless B_s Decays

A method based on flavour SU(3) is proposed for identifying and extracting New Physics (NP) amplitudes in charmless $ΔS=1$ $B_s$ decays using time-dependent CP asymmetries in these decays and in flavour SU(3) related $ΔS=0$ decays. For illustration, we assume a hierarchy, $\sim 1: λ: λ^2$ ($λ=0.2$), between a dominant $ΔS=1$ penguin amplitude, a NP amplitude and a Standard Model amplitude with weak phase $γ$. An uncertainty from SU(3) breaking corrections, reduced by using ratios of hadronic amplitudes, is further suppressed by a factor $λ$. We discuss examples for pairs of decays into two neutral vector mesons, $B_s\toϕϕ, B_s\toϕ\bar K^{*0}$ and $B_s\to K^{*0}\bar K^{*0}, B^0\to K^{*0}\bar K^{*0}$, where the magnitude of the NP amplitude, its weak and strong phases can be determined.

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arXiv2007

Exploring CP Violation and Penguin Effects through $B^0_d \to D^+ D^-$ and $B^0_s \to D^+_s D^-_s$

The decay $B^0_d \to D^+ D^-$ offers an interesting probe of CP violation, but requires control of penguin effects, which can be done through $B^0_s \to D^+_s D^-_s$ by means of the $U$-spin flavour symmetry of strong interactions. Recently, the Belle collaboration reported indications of large CP violation in the $B^0_d$ decay, which were, however, not confirmed by BaBar, and first signals of the $B^0_s$ channel were observed at the Tevatron. In view of these developments and the quickly approaching start of the LHC, we explore the allowed region in observable space for CP violation in $B^0_d \to D^+ D^-$, perform theoretical estimates of the relevant hadronic penguin parameters and observables, and address questions both about the most promising strategies for the extraction of CP-violating phases and about the interplay with other measurements of CP violation and the search for new physics. As far as the latter aspect is concerned, we point out that the $B^0_{q} \to D_{q}^+ D^-_{q}$ system provides a setting for the determination of the $B^0_q$-$\bar B^0_q$ mixing phases ($q\in\{d,s\}$) that is complementary to the conventional $B^0_d\to J/ψK_S$ and $B^0_s\to J/ψϕ$ modes with respect to possible new-physics effects in the electroweak penguin sector.

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arXiv2007

$B_{s,d} \to ππ,πK, KK$: Status and Prospects

Several years ago, it was pointed out that the U-spin-related decays $B_d\toπ^+π^-$, $B_s\to K^+K^-$ and $B_d\toπ^\mp K^\pm$, $B_s\to π^\pm K^\mp$ offer interesting strategies for the extraction of the angle gamma of the unitarity triangle. Using the first results from the Tevatron on the $B_s$ decays and the B-factory data on $B_{u,d}$ modes, we compare the determinations of gamma from both strategies, study the sensitivity on U-spin-breaking effects, discuss the resolution of discrete ambiguities, predict observables that were not yet measured but will be accessible at LHCb, explore the extraction of the width difference $ΔΓ_s$ from untagged $B_s\to K^+K^-$ rates, and address the impact of new physics. The data for the $B_d\toπ^+π^-$, $B_s\to K^+K^-$ system favour the BaBar measurement of direct CP violation in $B_d\toπ^+π^-$, which will be used in the numerical analysis, and result in a fortunate situation, yielding $γ=(66.6^{+4.3+4.0}_{-5.0-3.0})^\circ$, where the latter errors correspond to a generous estimate of U-spin-breaking effects. On the other hand, the $B_d\toπ^\mp K^\pm$, $B_s\to π^\pm K^\mp$ analysis leaves us with $26^\circ\leqγ\leq70^\circ$, and points to a value of the $B_s\to π^\pm K^\mp$ branching ratio that is larger than the current Tevatron result. An important further step will be the measurement of mixing-induced CP violation in $B_s\to K^+K^-$, which will also allow us to extract the $B^0_s$--$\bar B^0_s$ mixing phase unambiguously with the help of $B_s\to J/ψϕ$ at the LHC. Finally, the measurement of direct CP violation in $B_s\to K^+K^-$ will make the full exploitation of the physics potential of the $B_{s,d}\to ππ, πK, KK$ modes possible.

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